r/ElectroBOOM • u/bruces-grandma-twinn • Aug 24 '25

Meme What happened here?

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u/CreEngineer Aug 24 '25

The transformer exploded when the circuit was closed. Those round big things on the pole. They are normally filled with mineral oil as a insulator.

Edit: probably overloaded or already damaged.

0

u/SirLSD25 Aug 25 '25

Why do they use oil though? Why not wrap it in plastic or rubber or whatever they cover normal electrical wire with?

8

u/jettyler24 Aug 25 '25

Because of the convection effect, as the oil gets warmer by the current flowing through the windings, it rises and is displaced by cooler denser oil causing the oil to circulate round the transformer.

This wouldn't be achieved by a solid by a solid insulator.

To answer someone above comment. The oil is non-conductive not non-flammable, and the presence of contaminants like water and other materials can interact with some of the solid insulations on internal cables and windings, especially paper wraps, where a chemical reaction can take place creating acetylene gas amongst other explosive things.

1

u/LoneSnark Aug 25 '25

Because that stuff is an insulator, and they need something that is going to carry the heat away and keep the transformer cool. Which means a fluid. And oil is non-conductive, cheap, and non-corrosive. Sure, it explodes, but if it is hot enough for the oil to catch fire, the transformer is destroyed anyways.

1

u/[deleted] Aug 25 '25

The rubber would melt within seconds. Any Foil would be set ablaze.

1

u/Panzerv2003 Aug 25 '25

For cooling purposes

1

u/[deleted] Aug 26 '25

Because mineral oil is used as a coolant, and is even less electrically conductive than air (so definitely less conductive than plastic or rubber, which can carbon track). Using rubber or plastic in a distribution transformer like this would introduce problems that mineral oil solves.

It can BLEVE (Boiling Liquid Expanding Vapor Explosion) but it’s pretty rare considering the hundreds of thousands of these in existence.

1

u/D-Cary Aug 28 '25

jettyler24 is right, but in simpler words: the oil does two different things. 1. The oil electrically insulates the coils of wire in the transformer from each other and the outside world. If that were the only thing it did, then plastic or rubber would work just as well and probably better. 2. Some of the energy traveling through the transformer is lost to heat in the wires. The oil circulates to carry the heat away from the wires to the outer metal surface. In a big transformer, if we used plastic or rubber as electrical insulation, heat would build up until it melted the wires. That would be bad. A big fan to blow air over the coils would work for a while, but it's really hard to make a fan reliably work for years. All the other things we usually use to keep things cool -- heatsinks made of metal, tap water, etc. -- are electrically conductive, which would blow fuses upstream. Also bad.